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Climate change is expected to impact the geographic distribution of marsupial species in the near future and this impact is likely to be accentuated for the more specialist species. The water opossum (Chironectes minimus) is the only semiaquatic marsupial in the world and is considered naturally rare throughout its geographical range. In the present study, we use ecological niche modeling (ENM) to predict the potential impacts of climate change on the geographic distribution of water opossum throughout Neotropical Region at the end of twenty-first century. We assess the vulnerability of this species by calculating its biotic velocity and identifying potential areas for the conservation of the water opossum based on the changes in climatically stable areas over time. These areas were also compared with the availability of remnant forest in the future. The area of potential distribution of the water opossum is projected to decrease 22% in the future. Water opossum populations will be more vulnerable to climate change in central Brazil, toward the southern extreme, and in some regions of the Amazon biome. In the future, C. minimus may be unable to colonize some areas in southern South America and in Mexico. Climatically stable areas are found in Central America, northwestern and coastal areas in northern South America, and southeastern Brazil, however, most of these areas will not have remnant forest in the future. Climatically stable areas with remnant forest areas are an opportunity for the development of effective long-term conservation measures for C. minimus.

Genus Chironectes Illiger, 1811 TYPE SPECIES: Lutra minima Zimmermann, 1780, by monotypy. SYNONYMS: Gamba Liais, 1872; Memina G. Fischer, 1814. REMARKS: See Voss and Jansa (2009) for an emended generic description. This genus contains only a single species, the water opossum, Chironectes minimus. Although the results of morphometric analyses have sometimes been interpreted as evidence for multiple species of water opossums (Damasceno and Astúa, 2016; Cerqueira and Weber, 2017), the remarkable genetic similarity among specimens collected at widely scattered localities from Central America to southeastern Brazil suggests recent range expansion or widespread gene flow (Voss and Jansa, 2018)., Published as part of Voss, Robert S., 2022, An Annotated Checklist Of Recent Opossums (Mammalia: Didelphidae), pp. 1-77 in Bulletin of the American Museum of Natural History 2022 (455) on page 33, DOI: 10.1206/0003-0090.455.1.1, http://zenodo.org/record/7161371

Chironectes minimus (Zimmermann, 1780) TYPE MATERIAL AND TYPE LOCALITY: No type material is known to exist. This species is based on Buffon’s description of an animal from Cayenne (4.93° N, 52.33° W), French Guiana. SYNONYMS: argyrodytes Dickey, 1928; bresslaui Pohle, 1927; cayennensis Turton, 1800; guianensis Kerr, 1792; gujanensis Link, 1795; langsdorffi Boitard, 1842; palmata Daudin, 1802; panamensis Goldman, 1914; paraguensis Kerr, 1792; saricovienna Shaw, 1800; variegatus Olfers, 1818; yapock Desmarest, 1820. DISTRIBUTION: Chironectes minimus occurs from southern Mexico throughout most of the rainforested lowlands of Central America to South America; in South America it has been reported from most humid-tropical and -subtropical lowland biomes from Colombia southward to eastern Paraguay, northeastern Argentina (Misiones), and southern Brazil (Rio Grande do Sul). Recent collections from the Cerrado and the Pantanal were mapped by Brandão et al. (2015) and Antunes et al. (2021), respectively. Most range maps (e.g., Stein and Patton, 2008a: map 5) suggest that C. minimus does not occur in central Amazonia, but several central Amazonian specimens and observations indicate that it probably occurs throughout the region (Voss et al., 2019). REMARKS: The emended generic description provided by Voss and Jansa (2009) serves equally as a description of this species. Although several of the names listed above as synonyms have been recognized as valid subspecies by authors (e.g., Stein and Patton, 2008a), the absence of substantial genetic variation among geographic populations of water opossums (Voss and Jansa, 2018) suggests that a trinomial nomenclature is unnecessary., Published as part of Voss, Robert S., 2022, An Annotated Checklist Of Recent Opossums (Mammalia: Didelphidae), pp. 1-77 in Bulletin of the American Museum of Natural History 2022 (455) on page 33, DOI: 10.1206/0003-0090.455.1.1, http://zenodo.org/record/7161371, {"references":["Pohle, H. 1927. Uber die von Prof. Bresslau en Brasilien gesammelten Saugetiere (ausser den Nagetieren). Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft 40: 239 - 247.","Brandao, M. V., G. S. T. Garbino, L. P. Godoy, L. A. da Silva, and W. Pascoal. 2015. New records of Chironectes minimus (Zimmermann, 1780) (Didelphimorphia, Didelphidae) from central Brazil, with comments on its distribution pattern. Mammalia 79: 363 - 368.","Antunes, P. C. et al. [11 additional coauthors]. 2021. Marsupiais da Bacia do Alto Paraguai: uma revisao do conhecimento do planalto a planicie pantaneira. Boletim do Museu Paraense Emilio Goeldi Ciencias Naturais, Belem 16: 527 - 577.","Voss, R. S., D. W. Fleck, and S. A. Jansa. 2019. Mammalian diversity and Matses ethnomammalogy in Amazonian Peru. Part 3. Marsupials (Didelphimorphia). Bulletin of the American Museum of Natural History 432: 1 - 87."]}

The water opossum (Chironectes minimus) is a semi-aquatic mammal that is infrequently sampled in Atlantic rainforest areas in Brazil. Here we report on new records of C. minimus in the state of São Paulo, southeastern Brazil, and comment on its behavior and ecology. We placed nine camera traps in culverts and cattle boxes under a highway, between 2017 and 2019. From a total of 6,750 camera-trap-days, we obtained 16 records of C. minimus (0.24 records/100 camera-trap-days) in two cameras placed in culverts over streams. Most of the records were made between May and August, in the dry season and in the first six hours after sunset. The new records are from a highly degraded area with some riparian forests. The records lie approximately 30 km away from the nearest protected area where the species is known to occur. We suggest that C. minimus has some tolerance to degraded habitats, as long as the water bodies and riparian forests are minimally preserved. The new records presented here also fill a distribution gap in western São Paulo state. Resumo A cuíca d’agua (Chironectes minimus) é um mamífero semiaquático pouco amostrado em áreas de Mata Atlântica do Brasil. Neste estudo apresentamos novos registros de C. minimus no estado de São Paulo, sudeste do Brasil, e comentamos sobre seu comportamento e ecologia. Nós instalamos nove armadilhas fotográficas em drenagens fluviais e passagens de gado sob uma rodovia, entre 2017 e 2019. De um total de 6.750 armadilhas-fotográficas-dia, obtivemos 16 registros de C. minimus (0,24 registros/100 armadilhas-fotográficas-dia) em duas armadilhas fotográficas instaladas em drenagens fluviais. A maioria dos registros foram feitos entre maio e agosto, na estação seca, e nas seis primeiras horas da noite. Os novos registros são de uma área altamente degradada que possui algumas matas ciliares. Os registros estão a aproximadamente 30 km da área protegida mais próxima onde a espécie já foi registrada. Nós sugerimos que C. minimus possui certa tolerância a hábitats degradados, contanto que os corpos d’agua e as matas ciliares estejam minimamente preservados. Os novos registros aqui apresentados também preenchem uma lacuna amostral no oeste de São Paulo.

The water opossum (Chironectes minimus) is an elusive and solitary Neotropical semi-aquatic species, whose population dynamics cannot be studied using traditional methods to capture small mammals. Therefore, some aspects of its distribution, habitat requirements, and abundance are mostly unknown; which makes a proper determination of its conservation status difficult. Considering that new techniques known as species distribution models (SDMs) allow us to estimate the suitable areas and the most important variables for the distribution of a species, we compiled water opossum occurrences and modeled its potential distribution on a continental scale. We performed a SDM for the water opossum using MaxEnt and assessed the extent of habitat loss (km2) and the importance of Protected Areas (PAs). We compared the suitability values within and outside PAs using a Kolmogorov-Smirnov (KS) test to evaluate the efficiency of PAs. The results obtained were compared with the IUCN historical water opossum’s map. Additionally, we identified gaps in the potential distribution where for future surveys should be focused. We obtained models that describe the distribution of this species based on 292 occurrences with new information for 16 countries. Deforestation reduced the area of suitable habitat by ~40 % and only ~18 % corresponds to natural forest within PAs. Areas inside PAs showed higher suitability values (0.351 ± 0.276; P < 0.001) than areas outside them. We identified gaps within the distribution that need attention during future surveys such as the frontier between Venezuela and Guyana, the Amazonian region, and central-eastern Brazil. Our results showed areas absent in the IUCN’s distribution map, indicating that it needs to be updated. Thus, we proposed a new tentative extent of the water opossum distribution information here obtained. We demonstrated that PAs included areas with high habitat suitability values for C. minimus, which could protect the water opossum in the medium and long-term. Modifications to the physicochemical characteristics of the habitat due to forest loss and fragmentation can considerably affect water opossum populations and reduce local diversity. Thus, the preservation of river ecosystems and surrounding areas represents a necessary step for the conservation of C. minimus.

This report is the third in our monographic series on mammalian diversity and Matses ethnomammalogy in the Yavari-Ucayali interfluvial region of northeastern Peru. Based on taxonomic analysis of specimens collected in the region, we document the occurrence of 19 species of marsupials in the genera Caluromys, Glironia, Hyladelphys, Marmosa, Monodelphis, Metachirus, Chironectes, Didelphis, Philander, Gracilinanus, and Marmosops. Our principal taxonomic results include the following: (1) we provide a phylogenetic analysis of previously unpublished mitochondrial DNA (mtDNA) sequence data for Caluromys that supports the reciprocal monophyly of all currently recognized species in the genus but reveals substantial heterogeneity in one extralimital taxon; (2) we explain why Marmosa constantiae is the correct name for the southwestern Amazonian taxon previously known as Mar. demerarae, and we diagnose Mar. constantiae from Mar. rapposa, a superficially similar species from southern Peru, eastern Bolivia, and central Brazil; (3) we explain why Mar. rutteri is the correct name for one of the Amazonian species currently known as Mar. regina, and we restrict the latter name to the transAndean holotype; (4) we recognize Metachirus myosuros as a species distinct from Met. nudicaudatus based on morphological comparisons and a phylogenetic analysis of new mtDNA sequence data; and (5) we name a new species of Marmosops to honor the late Finnish-Peruvian naturalist Pekka Soini.Of the 19 marsupial species known to occur in the Yavari-Ucayali interfluve, 16 have been recorded in sympatry at Nuevo San Juan, the Matses village where we based most of our fieldwork from 1995 to 1999. We explain why we believe the marsupial species list from Nuevo San Juan to be complete (or nearly so), and we compare it with a species list obtained by similarly intensive fieldwork at Paracou (French Guiana). Although Nuevo San Juan and Paracou are 2500 km apart on opposite sides of Amazonia, the same opossum genera are present at both sites, the lists differing only in the species represented in each fauna. We briefly discuss current explanations for spatial turnover in species of terrestrial vertebrates across Amazonian landscapes and provide evidence that the upper Amazon is a significant dispersal barrier for marsupials.Marsupials are not important to the Matses in any way. In keeping with their cultural inattention to mammals that are inconspicuous, harmless, and too small to be of dietary significance, the Matses lexically distinguish only a few kinds of opossums, and they are not close observers of opossum morphology or behavior.

La Chucha de Agua, Chironectes minimus, es quizás uno de los marsupiales más crípticos en el Neotrópico. A pesar de que cuenta con registros puntuales sobre su presencia a lo largo de su distribución, sus reportes son escasos en ecosistemas circundantes a zonas periurbanas. Aquí reportamos una nueva localidad de presencia para la especie al suroriente del Valle de Aburrá, Antioquia, Colombia. A partir de análisis de los patrones actividad, se identificó que la especie presentó una tendencia nocturna, principalmente entre las 19h00 y las 00h00. Con respecto a la revisión y sobre su distribución altitudinal, a pesar de que existen registros a diferentes intervalos altitudinales, los registros sobre los 2.000 msnm son escasos. Reportamos un registro a 2.660 msnm y corroboramos uno a 2.562 msnm en el área de estudio. Igualmente, a partir de la revisión resaltamos el registro de mayor altitud a 2.800 msnm el cual ampliaría su rango actual.

The water opossum Chironectes minimus is the world’s only semi-aquatic marsupial. It is considered rare, and it is reported on several regional conservation lists of species as either endangered or data deficient. Given its uniqueness and the poor knowledge of its ecology, we aimed to investigate home range size and overlap and habitat selection of the water opossum in Atlantic Forest streams in southeastern Brazil. We radio tracked water opossums and collected information about their habitats and behaviour from October 2004 to April 2010. We combined common home range estimators for animals living in linear habitats with the synoptic model of home range and habitat selection. For the 10 individuals monitored, the home ranges varied between 0.80 and 9.66 km of watercourses; none of them had exclusive home ranges. The home range size for males was, on average, three times larger than for females. The overlap data showed that, on average, one male could encompass the home ranges of up to five females simultaneously, but more than one male could have access to the same female. For habitat selection at the individual level, we could not find any strong influence of habitat features on water opossum preferences because individuals selected different sets of habitat variables. However, at the population level, we found a negative relationship between home range size and river size. The water opossum seems to prefer shallow and narrow watercourses to establish its home ranges. Here, we present valuable information to advance our knowledge of the water opossum and its ecology, which is urgent for conservation purposes.

The Water Opossum, Chironectes minimus (Didelphimorphia, Didelphidae), is the only semi-aquatic marsupial and can be easily identified for its uniquely patterned water resistant pelage and webbed hind-feet. The species is distributed along the Neotropical region (from Southern Mexico to Northwestern Argentina) and is currently divided on four subspecies (C.m. argyrodytes, C. m. panamensis, C. m. minimus, C. m. paraguensis), based on its geographical distribution. We evaluated the geographic variation in C. minimus, using traditional and geometric morphometrics techniques to capture the size and shape of the skull to identify differences between the populations that could relate to existing subpsecies or populations that and would merit particular taxonomic attention. We took 13 skull measurements, and digitized 37, 18, and 23 2D landmarks on the dorsal and lateral view of the cranium and on the lateral view of the mandible, respectively. The sample consisted on 135 individuals from 66 localities. Analyses of both datasets showed that the Southern South America and Northern Central America animals differ from the other populations. Geometric morphometrics shows on the three views that the Amazon animals differ from the others probably due to existing geographical barriers. These morphological differences among populations of the Water Opossum support the need for a proper phylogenetic assessment of these populations, in order to clarify their taxonomic status.

We studied phenotypic variation in water opossum Chironectes minimus through morphological variation in size and shape of 16 cranial characters among six groups of populations of Chironectes defined by a transect analysis named according their main distributions: Central America, Venezuela/Colombia, Guianas, Belem, Bolivia/Peru, and Atlantic Forest. We also studied environmental variation among the groups and the influence of temperature seasonality and minimum temperature of coldest month on the body size of C. minimus. Morphometric differences in both size and shape were sharp between two major groups: Atlantic Forest and Central America+Venezuela/Colombia+Belem. The same pattern of differentiation was also observed in the environmental variables each group experiences. We also found a negative relationship between body size and temperature seasonality which showed that C. minimus follows a converse Bergmann’s rule cline. Our results on morphometric and environmental space suggest that specimens from the Atlantic Forest are different from specimens from Central America+Venezuela/Colombia+Belem both in size and shape and environmentally. We suggest that these major groups may comprehend different clades but a proper taxonomic assessment is needed to confirm our hypothesis.

A comparative study of limb morphology indicates that the osteological and myological differences between Didelphis virginiana, the Virginia opossum, and Chironectes minimus, the water opossum, may be associated in Chironectes with decreased resistance to water and increased mechanical advantage of its muscles for increased force. Limb myology is described and a synonymy of terms is applied to the musculature of these two opossums.

We evaluated the selection of resting sites occupied by the water opossum Chironectes minimus, between 2004 and 2010, in streams of the Brazilian Atlantic Forest. Fourteen radio-tracked adult (males and females) opossums used natural cavities as resting sites. Opossums selected narrow river stretches and selected their resting sites mainly according to characteristics favoring protection against adverse weather conditions. Likewise, opossums avoided disturbed habitats and established their resting sites in well-preserved riparian forest sites, selecting river sections containing a high density of trees and a high proportion of forest cover between the river banks and 50 m from the river. Besides increasing our knowledge on this species habitat selection, such findings further highlight this species’ sensitivity to human disturbance.

The activity of the water opossum Chironectes minimus was studied in Atlantic forest rivers in south-eastern Brazil using radiotracking, from October 2004 to October 2008. There were 439 nocturnal fixes of 11 males and four females. Activity patterns of the water opossum were compared among sexes and seasons, using linear and generalized linear mixed models. The water opossum is active mostly at night, showing a unimodal pattern, with activity increasing after sunset and decreasing thereafter along the night. Females were more active in the first quarter of the night and males in the second one. The activity period of males was longer in the dry season, while for females it was longer in the wet season. Sex and season were important determinants of the water opossum activity patterns, mainly because of different sex strategies in a promiscuous/polygynous mating system. However, despite those influences the overall distribution of activity along the night was similar to most Neotropical marsupials. Therefore, similarities in the activity patterns are probably due to phylogenetic constraints and to the absence or weakness of selective pressures modifying the activity of the water opossum.

Riparian zones, as spatially constrained environments, can favor intense competition among similar species and thus the occurrence of spatial segregation. We investigated the spatial pattern of water opossum Chironectes minimus and water rat Nectomys squamipes captures in Atlantic Forest rivers in southeast Brazil. Our goals were to test if the water opossum and water rat are spatially segregated, to describe the habitat selection by these two species and to verify if habitat degradation favors the water rat, at the expense of water opossum. The abundances of water opossum and water rat were negatively correlated. Water opossum abundance was higher in wide rivers with high tree density in the riverbank, while water rat abundance was higher in narrow streams within non-forested areas. The ratio between the water opossum and water rat relative abundances was positively related to the degree of conservation of the riverine habitat. The segregation showed by the water opossum and the water rat was produced by their morphological and ecological differences, rather than by interespecific competition. Based on ours results we predict that deforestation, especially the removal of riparian vegetation, will result in a reduction of the suitable habitat for the water opossum while the water rat will expand its range.

We studied the population structure, spatial patterns, and activity patterns of the water opossum (Chironectes minimus) via capture–mark–recapture and radiotelemetry from October 2004 to October 2006 in Atlantic Forest streams in southeastern Brazil. We tested the hypothesis of reproductive seasonality, the usual pattern in neotropical marsupials, by examining recruitment of juveniles. The hypothesis was rejected, supporting the alternative hypothesis that breeding by water opossums was better explained by its habitat characteristics and prey availability than by its phylogenetic ancestry. The observed sex ratio was significantly biased toward males. The home lengths of individual water opossums varied from 844 to 3,724 m. Males had larger home lengths than females, and there were male–male and male–female overlaps. The longer home lengths for males may explain the observed sex ratio bias, because males are more exposed to capture. All individuals used stream stretches with preserved riparian for...

49. Water Opossum Chironectes minimus French: Yapock / German: Schwimmbeutler / Spanish: Zariglieya acuética Other common names: Yapok Taxonomy. Lutra minima Zimmermann, 1780, “Gujana.” Restricted by A. Cabrera in 1958 to “ Cayenne, French Guiana.” A taxonomic revision using modern techniques may change the status of subspecies. Four subspecies recognized. Subspecies and Distribution. C.m.minimusZimmermann,1780—E&SEColombia,Venezuela(SoftheOrinocoRiver),andtheGuianastoNBrazil(EtoNWMaranhao),alsoWAmazonianBrazil,EEcuador,EPeru,andW&CBolivia. C.m.argyrodytesDickey,1928—SMexico(SofOaxacaandTabasco)andNCentralAmerica. C.m.panamensisGoldman,1914—SNicaraguathroughCostaRicaandPanama,toN&WColombia,NVenezuela,TrinidadI,andSintoWEcuadorandNWPeru. C. m. paraguensis Kerr, 1792 — S & SE Brazil, E Paraguay, N Uruguay (Cerro Largo), and NE Argentina (Misiones). Descriptive notes. Head-body 25-40 cm, tail 27-43 cm; weight 510-790 g. The Water Opossum is possibly the most distinctive species of Didelphidae, both ecologically and morphologically. Its fur pattern is unique. Dorsal fur is pale silvery gray, with four blackish transverse bars (located over shoulders and on center of back, hips, and lower rump) connected by blackish mid-dorsal stripe that runs from crown to base of tail. Shoulder and rump patches extend laterally over legs. Head fur is blackish, with dark eye-rings continuous with blackish crown fur, resulting in pale bar over each eye. Tail length is c.110% of head-body length, and tail is round and has fur on proximal onesixth or less. Naked rest of tail is blackish with a whitish tip. Ventral fur is pure bright white. Fur is short, dense, smooth, and water-repellent. Feet are reddish-brown or dark gray, with fleshy carpal tubercles in both sexes, and hindfeet are fully webbed from base to terminal phalanges. Ears are moderately large, naked, and rounded. Females have a distinct pouch that opens backward and can be tightly closed. Five mammae are present, two on each side, and a medial mamma. Water Opossums are the only species of opossums with distinct urogenital and rectal openings rather than a single cloacal opening. Male Water Opossums also have a rudimentary “pouch” anterior to the scrotum. Cremaster muscle in tunica vaginalis allows scrotum to be pulled up and kept in contact with abdominal body wall, at the rudimentary pouch area, so pouch protects scrotum while a male is swimming and diving or even moving on land. The Water Opossum has a 2n = 22, FN = 20 karyotype, with all acrocentric autosomes, and with an acrocentric X-chromosome similar in size to autosomes and a small acrocentric Y-chromosome. Skull shape is sexually dimorphic. Habitat. Tropical and subtropical habitats, with permanent water (rivers, streams, and ponds), including moist lowland and lower montane forests, from sea level up to elevations of 1860 m. Water Opossums inhabit slow and fast-flowing waters but are normally absent from waters with high levels of sediment. In south-eastern Brazil, they occur only in fast-flowing streams, preferring wide waterways with dense forest on banks and stones on bottom. In cerrado, Water Opossumsare found near ponds or in gallery forests. Food and Feeding. Due to its semi-aquatic habitat, the Water Opossum is also unique in its foraging habits. It swims by paddling with hindfeet only, while keeping forefeet extended forward, fingers wide open, feeling substrate for prey. Prey is often captured with hands and then brought to the bank to be eaten. They have larger digital pads and reduced claws compared with other big-bodied species of opossums. Fingertips of Water Opossums have epidermal scales surrounded by finger-like conical structures that are radially oriented, enabling perception of tactical stimuli from all directions. These structures, along with less-clawed fingertips, likely improve tactile abilities underwater. Diet of the Water Opossum includes mostly aquatic or semi-aquatic vertebrates (fish, particularly slow-moving and bottom-dwelling species such as silurids and cichlids, and frogs) and aquatic invertebrates (crustaceans and mollusks) but also crickets; occasionally, fruits and aquatic plants have been found. Water Opossums were also seen opportunistically preying on bats (Seba’s Short-tailed Bat, Carollia perspicillata, and the Little Yellow-shouldered Bat, Sturnira lilium) that were entangled in a mist-net set over a stream. Captive individuals readily consumed freshly killed mice, chicks, young rats, and crayfish, and they also fed on slices of fish or meat mixed with cod-liver oil and chopped meat. Consumption offish eggs has also been reported. Nutritional contents of preferred diets, determined with cafeteria experiments in captivity where individuals were free to choose food items according to their needs, resulted in 8 g of proteins, 7-1 g of carbohydrates, 0-8 g oflipids, and 2-:2% offibers per 100 g of dry matter. Breeding. Nests of the Water Opossum are located in chambers at the end of tunnels that are ¢.60 cm long. Entrances to tunnels are just above water level. Like other species of opossums, the Water Opossum usesits tail to drag material for nest building. Nest entrances have a diameter of c.10 cm and can found not only on banks of waterways but also on the ground, among rocks, or among roots. The nest is lined with leaves and grass. Pre-copulatory behavior of the Water Opossum is similar to that of other species of opossums, with males circling or chasing females and engaging in oral-genital contact. Males also grab females during copulation. Reported litter sizes vary from one to five young, but only 2-4 young/litter were observed in south-eastern Brazil. Pouch young are apparently tolerant of low oxygen levels and resistant to asphyxia, enabling the mother to dive while carrying young in her pouch. This may not be unique to Water Opossums because Virginia Opossums also dive and swim underwater with pouch young. In Brazil, young are born in December—January, and females are found with pouch young in January-February. In Argentina, there are records of young born in August, and in Venezuela, females with pouch young were captured in January, July, and November. Throughout the distribution of the Water Opossum, females with pouch young are captured all year long, suggesting that they do not breed seasonally. Young detach from mammae at c.48 days but continue to nurse. As in other big-bodied species of opossums, the female sometimes carries large young on her back. Juveniles have been seen swimming with their mothers in the wild. Activity patterns. Water Opossums are nocturnal. They become active right after sunset and concentrate their activity during the first one-half of the night; during this period, males and females have alternate preferred foraging times, with males more active during the first one-half of the activity period and females during the second one-half. Males have longer activity periods during the dry season, and females have longer activity periods during the wet season. Movements, Home range and Social organization. Water Opossums swim in a unique way. All other opossums that have been seen swimming use all four legs to paddle, but the Water Opossum paddles with hindfeet only, in an alternate stroke. Water-repellent fur provides additional buoyancy, and they are able to swim keeping their backs almost parallel to water surface, with entire head and back above water level. Speed ranges from 0-7 km/h to 2:6 km/h. Water Opossums usually flee from danger by swimming, but some individuals have been seen leaving water and escaping into dense streamside vegetation or entering a burrow. They also reportedly splash noisily while wading or swimming. Captive individuals have been seen jumping and climbing with agility on vertical supports, sometimes to reach hollow logs above ground level that were used as dens. Home ranges are linear, and lengths in south-eastern Brazil are 844-3742 m along rivers. Densities are hard to compare with other opossums because they relate to river length and not area, but current estimates can be up to 1-3 ind/km. Home ranges of male Water Opossums are up to four times longer than those of females, and there is considerable overlap of home ranges within and between sexes. Water Opossums are solitary, although in a single situation two individuals (one male and one female) were found sharing a den. Although some captive individuals did not tolerate presence of another individual, mutual grooming has been observed in captivity after swimming, and in some cases, up to three adults shared the same enclosure without any agonistic activity. Status and Conservation. Classified as Least Concern on The [UCN Red List. The Water Opossum has a wide distribution and presumably a large population, and it occurs in several protected areas. They are sometimes considered rare, but this is probably due to difficulty of locating and capturing them. Populations of Water Opossums are not only threatened by deforestation, as are most forest-dwelling species, but additionally by contamination and deterioration of freshwater ecosystems. Artisanal gold mining in French Guiana and other parts of the distribution of the Water Opossum might degrade watercourses, posing a serious threat. Bibliography. Abdala et al. (2006), Alho et al. (1986), Ardente et al. (2013), Astua (2010), Astua, Lemos & Cerqueira (2001), Astua, Santori et al. (2003), Brandao, Garbino et al. (2014), Bressiani & Graipel (2008), Breviglieri & Pedro (2010), Cabrera (1958), Carvalho et al. (2002), Davis (1966), Eisenberg (1989), Emmons & Feer (1997), Fish (1993), Galliez & Fernandez (2012), Galliez et al. (2009), Gardner (2005), Gonzalez & Fregueiro (1998), Graipel et al. (2006), Hamrick (2001), Handley (1976), Julien-Laferriere (1991), Leite et al. (2013), Mares & Braun (2000), Marshall (1978d), McNab (1982), Medellin (1991), Melo & Sponchiado (2012), Mondolfi & Medina (1957), Monteiro-Filho et al. (2006), Nogueira et al. (2004), Palma & Yates (1996), Redford & Eisenberg (1992), Reig et al. (1977), Rosenthal (1975), Salazar et al. (1994), Sidebotham (1885), Smith, P (2007b), Stein (1981), Stein & Patton (2007a), Streilein (1982a), Thompson (1988), Tortato (2009), Voss & Emmons (1996), Voss & Jansa (2009), Voss et al. (2001), Yensen et al. (1994), Yunis et al. (1972), Zetek (1930)., Published as part of Russell A. Mittermeier & Don E. Wilson, 2015, Didelphidae, pp. 129-186 in Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona :Lynx Edicions on pages 157-158, DOI: 10.5281/zenodo.6685333

Chironectes minimus is a marsupial with unique morphological and ecological characteristics. Owing mainly to its semi-aquatic habits, it is rarely col- lected by conventional methods, being consequently underrepresented in scientific collections. Its distribu- tion in South America is currently considered disjunct, with a north-west and a south-east portion, and a large gap of more than one thousand kilometers that com- prises central Amazonia and a large portion of the Cer- rado. On the basis of four museum specimens and two photographed live animals, we present six new records for the species. These records extend the species ' distri- bution, showing that its range is continuous from south- ern Amazonia and through Cerrado gallery forests, to the southern portion of its range in southeastern South America. Most known records of C. minimus are from preserved riparian forests that usually present certain characteristics, such as fast-flowing water, stony sub- strate, and/or natural holes used as dens. Therefore, we hypothesize that the occurrence of this species is more closely related to well-preserved riparian forests con- taining these types of habitats than to the biomes them- selves. Consequently, this species is probably found through most tropical and subtropical South American biomes that present the aforementioned habitat types. Therefore, the previous distributional gap of the spe- cies, now filled on its central-east portion, was prob- ably a sampling artifact.

The male genital system was examined in 9 male specimens of Chironectes minimus (2 adult and 7 young) from Brazil. Unlike other didelphids, C. minimus lacks a cloaca and has distinct anal and urogenital openings, and the tunica vaginalis lacks black pigmentation. Similar to other American didelphids, C. minimus has a segmented carrot-shaped prostate gland with 3 anatomical segments that can be distinguished by color, length, and diameter in adults. The 2 pairs of bulbourethral glands of C. minimus are similar to those found in species of Caluromys, Gracilinanus, Monodelphis, Thylamys, and Glironia. The tip of each hemi-glans is rounded and bulbous shaped, whereas the urethral grooves end at the ventral aspect of the tip of each half glans.

Phenotypic evolutionary rates are reported for cranial characters of eight species of large-bodied Neotropical marsupials: Didelphis aurita, D. marsupialis, D. albiventris, Philander opossum, P. frenata, Lutreolina crassicaudata, Chironectes minimus, and Metachirus nudicaudatus. These rates were found to be lower than expected if cranial diversification in these opossums had occurred by mutation and genetic drift only, and it is clear that a greater diversification was prevented. As all parameters used in estimating rates were very conservative, the conclusion that stabilizing selection has predominated during the evolution of the skull of large-bodied opossums is fairly robust. We also show that directional selection sustained for 150 generations (158 years) or less is capable of producing differences of the same magnitudes as those found between various pairs of species. Therefore, we conclude that even where a particular differentiation has been caused by directional selection, neutral rate tests are unlikely to infer it. This is because following a morphological shift, stabilizing selection will progressively erase evidences of directional selection.

It has been suggested that the karyotype of the marsupials derived from a low diploid number (2n = 14) which originated, through fissions of biarmed chromosomes, the karyotypes with a higher 2n. The telomeric sequence (T2AG3)nwas in situhybridized to the chromosomes of Gracilinanus microtarsusand G. emiliae, Micoureus demeraraeand Marmosa murina, species with 2n = 14, in Monodelphissp., M. domestica, M. kunsiand M. brevicaudatawith 2n = 18, and in Lutreolina crassicaudata, Didelphis albiventris, Chironectes minimus, Philander opossumand P. frenata, all of them with 2n = 22. The probe hybridization occurred in the telomeric regions of both arms, short and long, of all chromosomes of the complement of all individuals of all species analysed. However, in some pairs of the karyotypes of Gracilinanus microtarsusand Micoureus demerarae(with 2n = 14), and in Monodelphissp., M. domestica, M. kunsiand M. brevicaudata(2n = 18) ectopic signs of hybridization were detected proximal to the centromeres, suggesting the retention of this telomeric sequence in the centromeric regions of some chromosomes of these species. Based on these results, it is proposed that the karyotype of marsupials evolved from a 2n = 22 to a 2n = 14, by means of chromosomal fusions.

The kinematics of surface swimming of the Virginia opossum (Didelphis virginiunu) and water opossum (Chironectes minimus) were studied to determine locomotor changes associated with the evolutionary transition from terrestrial to semiaquatic existence. Films of individual animals swimming across an aquarium were made and analyzed. Didelphis swam with a modified quadrupedal gait similar to a diagonal sequence run. Besides providing propulsive forces, this gait generated an upward force allowing the nasal apertures to remain above the water for breathing. In contrast, Chironectes paddled exclusively with the hind limbs in a manner similar to other semiaquatic mammals. The non-wettable fur of Chironectes seemed to provide sufficient buoyancy so that no additional forces were required to maintain the nares above the water surface. Transition to exclusive hind limb paddling in semiaquatic mammals appears to be associated with development of non-wettable fur for increased buoyancy and with increased swimming effectiveness resulting from lack of interference between forelimbs and hind limbs during the stroke cycle. Eliminating use of the forelimbs in paddling also permitted unrestricted movement of the hind limbs.

Early developmental and demographic events in many marsupials occur in the mother's pouch out of animal managers' sight. Because pouch examination is perceived as being stressful both to animal and handler, the pouch has proven to be a formidable physical and psychological barrier to the study of early life history events in marsupials in zoos. Demographic and developmental data such as litter size at birth, secondary sex ratios, infant mortality rates, and early rates of growth and development, normally considered essential information for the development of breeding programs, are therefore essentially unavailable for most zoo populations of marsupials. Here we describe a technique for the safe and non-stressful examination of the pouches of small (< 2 kg) marsupials that enables the capture of such data. The technique, involving the use of transparent plastic tubes of slightly different diameters for restraining the animals and an otoscope for examining the pouch and its contents, has been very successfully applied to life history studies of four species at the National Zoological Park: Pseudocheirus peregrinus, Petaurus breviceps, Philander opossum, and Chironectes minimus.

The tooth eruption and replacement sequence in Marmosa incana does not follow that described by Tyndale-Biscoe and Mackenzie (1976) for Didelphis marsupialis ; therefore, a modified system of dental age classes is proposed. Whereas, in Didelphis the first or deciduous molar (herein referred to as dP3) is shed and P3 erupts before the appearance of M4, in M. incana dP3 is retained until M4 is functional; four molariform teeth, therefore, are present at all times from class 4 onward. The same sequence occurs in many species of Marmosa (sensu lato), Monodelphis , and Caluromys , whereas the Didelphis pattern is followed by species of Philander, Chironectes, Lutreolina , and the microbiotheriid Dromiciops . The sequence in Metachirus is somewhat ambiguous. A possible inference is that Marmosa and Monodelphis belong with Caluromys in a monophyletic group, rather than with the other didelphids.

The purpose of this study was to investigate how didelphid marsupials have diversified in morphology of their claws and digital pads as they evolved different foraging preferences such as terrestrial, aquatic, and arboreal feeding behaviours. Both arboreal and more terrestrial didelphids have papillary ridges on the digital pads of the fore and hindfoot. In contrast, the papillary ridges on the pedal digital skin of the water opossum Chironectes minimus have been replaced by nonoverlapping, thickened epidermal scales. Chironectes also differs from the other didelphids studied in having finger tips with reduced claws and digital pads that are covered with raised epidermal scales having projecting, finger-like cones arranged radially around the perimeter of each scale. The reduced claws and unusual digit skin microstructure of Chironectes likely improve this animal's ability to recognise and identify live animal prey under water using only its sense of touch.

Chironectes Illiger, 1811. Prodr. Syst. Mammal. Avium., p. 76. TYPE SPECIES: Lutra minima Zimmermann, 1780, by monotypy. SYNONYMS: Gamba Liais, 1872; Mentina Fischer, 1814; Sarigua Muirhead, 1819 (part)., Published as part of Alfred L. Gardner, 1993, Order Didelphimorphia, pp. 15-23 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 16, DOI: 10.5281/zenodo.7353070, {"references":["Muirhead, L. 1819. Mazology. Pp. 393 - 486 [pls. 353 - 358], in The Edinburgh encyclopaedia, (D. Brewster, ed.). Fourth ed. William Blackwood, Edinburgh, 13: 1 - 744, pls. 347 - 371, 1830."]}

COLLINS, L. R. 1973. Monotremes and marsupials. A reference for zoological institutions. Smithsonian Inst. Press, Washington, D.C. HALL, E. R. 1981. The mammals of North America. Second ed. John Wiley and Sons, New York. HUNSAKER, D. 1977. Ecology of New World marsupials. Pp. 95-156, in The biology of marsupials (D. Hunsaker, ed.). Academic Press, New York. MARSHALL, L. G. 1978. Chiro ectes minimus. Mammalian Species, n . 109:1-6. McCARTHY, T. J. 1982. Chironectes, Cyclopes, Cabassous and probably Cebus in southern Belize. Mammalia, 46:397-400. McLEAN, R. G., C. H. CALISHER, AND G. L. PARHAM. 1987. Isolation of Cache Valley virus and detection of antibody for selected arborviruses in Michigan horses in 1980. Amer. J. Vet. Res., 48:1039-1041. UBICO, S. R. 1989. Viral infections of bats of Guatemala. Unpubl. M.S. thesis, Colorado State Univ., Fort Collins.

Marsupial standard metabolic rates (SMRs) average 70% of that predicted by Kleiber for domesticated eutherians. Only one marsupial, the water opossum (Chironectes minimus; Didelphidae) has been reported to have a level of metabolism near that (95%) predicted by Kleiber. This high SMR of Chironectes has been cited as evidence that marsupials are not phylogenetically constrained to low SMRs. Standard respirometry techniques were used to reexamine SMR, evaporative water loss (EWL), and heat transfer coefficients for four wild-caught water opossums (922 g) over a broad range of ambient temperatures (10-34 C). SMR was 64% of Kleiber's predicted value; this is 33% below that reported in an earlier study and 2% below the predicted value for a 922-g marsupial. Mean $T_{b}$ (35.7 C) and EWL (.700 mg g⁻¹ h⁻¹) in thermoneutrality were consistent with a low SMR. Neither body fat deposited while in captivity, duration in captivity, nor measurement error appeared responsible for differences from the previous study. Wet...

Examination of postcranial morphology in species of five murid rodent genera elucidated osteological and myological modifications associated with adaptation to a semiaquatic environment. Moreover, these differences exhibited a morphologic progression corresponding to the degree of external modifications in the semiaquatic taxa. Morphometric analyses of osteological measurements provided quantitative confirmation of these data. Although the majority of morphometric variation among genera was attributed to size, shape differences interpreted from variable loadings on the second principal component indicated that the semiaquatic rodents examined had long hind feet and long tails combined with short proximal elements relative to their terrestrial counterparts. This variation is similar to that reported for the semiaquatic opossum, Chironectes , in comparison to its terrestrial relative, Didelphis . Multivariate coefficients of allometry lent additional support to the hypothesis that the degree of morphologic adaptation exhibited by these semiaquatic mammals is in proportion to the amount of time the animals spend in the water and to the types of activities performed there.

Panniculus carnosus is well developed in the five Didelphids studied. It is described in three parts: pars dorsalis, pars thoracoabdominalis and pars pudenda, in Marmosa, Didelphis, Metachirops, Metachirus and Chironectes, and in Orolestes, a caenolestid marsupial. Pars dorsalis is well developed in all five genera, but not so well developed as in Orolestes; pars thoracoabdominalis is present in all five Didelphids, but not in Orolestes; and the degree of development of pars pudenda is correlated with the development of the pouch, being absent in Orolestes, weak in Marmosa and strong in both males and females of the other genera. In Chironectes, in which genus the male develops a pouch, pars pudenda is strikingly developed. The ‘sphincter marsupii’ of other writers is considered to be a portion of pars pudenda. In early development an epidermal ridge arises surrounding part of the mammary area. In Marmosa these ridges move laterally and posteriorly before the expanding mammary area. In Didelphis, Metachirops, Metachirus and Chironectes the ridges form the lips of the pouch. The pouch is formed when the ridges remain stationary and the expanding mammary area throws the skin into a double-walled fold.

Described as new, from larvae only, are: Ornithodoros (Alectorobius) casebeeri from the rodent, Ototylomys sp., in Costa Rica; O. (A.) chironectes from water opossum, Chironectcs minimus , and cotton rat, Sigmodon hispidus griseus , in Nicaragua; O. (A.) clarki from bats, Pteronotus davyi fulvus and P. suapurensis , in Nicaragua; O. (A.) knoxjonesi from bat, Balantiopteryx p. plicata , in Nicaragua; O. (A.) marmosae from murine opossum, Marmosa robinsoni , and mouse, Rhipidomys sp., in Venezuela and Colombia; O. (A.) tiptoni from bat, Noctilio leporinus , from Venezuela and O. (A.) tuttlei from paca, Agouti paca , and tapir, Tapirus terrestris , in Venezuela. In addition, the following species described by Kohls, Clifford, and Jones are now placed in the subgenus Alectorobius: O. setosus, O. eptesicus, O. peruvianus, O. peropteryx, O. mimon , and O. echimys .

SUMMARY. The hair tracts of Marmosa cinerea, M. murina, Chironectes minimus. Didelphis marsupialis var. azarae, Didelphis marsupialis var., Didelphis sp. and Metachirus oppossum, all members of the marsupial family Didelphidae are recorded. The several tract patterns are shown to be classifiable into a series of stages of increasing complexity in terms of divergent and convergent centres.

These karyotypes are gifts of Dr. Robert J. Baker. The specimens were captured in a locality approximately 12 Km north of Santa Barbara, Honduras. Bone marrow samples were used for cytological preparations. The voucher specimen numbers are ♂ 12599 and ♀ 12601, respectively, which are kept at Texas Tech University Museum, Lubbock, Texas, USA.

Chironectes Illiger, 1811. Prodr. Syst. Mammal, et Avium., p. 76. REVIEWED BY: J. Ramirez-Pulido (JRP). ISIS NUMBER: 5301402001003000000., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Marsupialia, pp. 18-51 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 18, DOI: 10.5281/zenodo.7353009

Chironectes minimus (Zimmermann, 1780). Geogr. Gesch. Mensch. Vierf. Thiere, 2:317. TYPE LOCALITY: French Guiana, Cayenne. DISTRIBUTION: Oaxaca and Tabasco (Mexico) to Peru, N.E. Argentina, S. and N.E. Brazil, French Guiana, Guyana, Surinam, and Trinidad. COMMENT: Reviewed by Marshall, 1978, Mamm. Species, 109:1-6. ISIS NUMBER: 5301402001003001001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Marsupialia, pp. 18-51 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 18, DOI: 10.5281/zenodo.7353009

We report a new record for the bushy-tailed opossum Glironia venusta Thomas, 1912 and the water opossum Chironectes minimus (Zimmermann, 1780) in the Floresta Nacional de Carajás, municipality of Parauapebas, state of Pará, Brazil (06°03'00" S, 50°15'00" W). This study represents the second record of Glironia venusta, but the first voucher specimen for eastern Brazilian Amazon. For Chironectes minimus, this record extends the range of the species 558 km southeastwards from the closest known locality in Pará.

A chromosome study of the didelphiids C. lanatus and Ch. minimus is presented. The karyotype of C. lanatus is very similar to that of Marmosa robinsoni but differs, in so . far as the X chromosome is concerned, from that of C. derbianus. As an explanation for the karyologic difference between the two Caluromys species we postulate a peri- centric inversion of the X chromosome passing from the acrocentric form of C. derbianus to the submetacentric of C. lanatus. The chromosomes of Ch. minimus (2n = 22) are all acrocentric and have a strong similarity to those described in the genera Didelphis and Philander, but the sexual chromosomes are larger and have an XY form of sexual complement.